This thesis examines two techniques for measuring two-phase flow parameters in an air/water system using intrusive conductivity probes. Specifically, the theoretical derivation for measuring void fraction and interfacial area using a two-sensor needle-type probe is derived, and a statistical analysis of the accuracy using the two-sensor probe for measuring interfacial...
The next generation of nuclear safety analysis computer codes will include detailed modeling of the interfacial area concentration. The interfacial area concentration is the essence of the two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links the two phases together...
Two-phase flow in a fractal-like branching microchannel heat sink may have
enhanced heat transfer capabilities over single phase flow in the same branching
channel network. In order to exploit this potential, a complete understanding
of flow boiling in this geometry is required. The fractal-like geometry is similar
to that of...
Two-phase gas-liquid flows in microscale fractal-like branching channel flow networks were experimentally studied to assess the validity of existing void fraction correlations and flow regimes based on superficial gas and liquid velocities. Void fractions were assessed using two different methods. First, void fraction data were acquired using a High-Speed-High-Resolution (HSHR)...
This paper describes a study of two-phase gas-liquid vertical
annular climbing film flow. Using a high speed Fastax movie camera,
motion was slowed sufficiently to facilitate detailed analysis of the
climbing film structure, based on single frame projections. The
dynamic characteristics of the liquid film could likewise be obtained,
though...
Momentum transfer in climbing-film flow in an annular duct was
investigated. Air and various liquids, with a wide range of viscosities
and surface tensions, were investigated. The two phases flowed co-currently
upward, the liquid climbing as a thin film on the inner wail
while the outer wall remained dry.
The...
The next generation of nuclear safety analysis computer codes will require detailed
modeling of two-phase fluid flow. The most complete and fundamental model used for
these calculations is known as the two-fluid model. It is the most accurate of the two-phase
models since it considers each phase independently and links...
An improved version of the one-dimensional horizontal two-fluid flow model has been developed by incorporating physical terms for gravity and local void fraction profiles. Introduction of an interface mixing layer concept allows the one-dimensional two-fluid model to remain hyperbolic. This will overcomes a major obstacle in using the current one-dimensional...
A phase distribution parameter has been added to the one-dimensional two-phase horizontal flow conservation equations. The phase distribution parameter was incorporated into the conservation equations in an attempt to add stability and remove correlation switching by incorporating gravity. Determination of the phase distribution parameter requires an average void fraction profile...
It is hypothesized that increases in pressure drop due to vapor generation during boiling in microchannels can be reduced by extraction of vapor at its point of inception. Ultimately, this local vapor extraction decreases the pressure drop required to drive the flow through a fractal-like branching, microchannel flow network within...
................................................................................. 100
LIST OF FIGURES
Figure Page
2.1
Typical two-phaseflow patterns in horizontal
Two-phase flows in microtechnology based devices are purposefully present in multiphase reactors, phase separators, analytical devices and others. Two-phase flows can also be an undesirable side effect occurring during operation due to phase transitions or, more commonly, introduction of surrounding air through equipment gaps and with process feed. In both...
Understanding the behavior of hydrophobic membranes is important for applications where separating a gas from a liquid-gas mixture is beneficial. For example, in-situ vapor extraction can be used in microscale heat sinks to improve heat transfer and flow stability. In this study, gas is experimentally evaluated flowing through flexible polytetrafluoroethylene...
The flooding phenomenon can be defined as the maximum attainable flow
condition beyond which the well defined countercurrent flow pattern can no longer
exist. Thus the countercurrent flow limit (CCFL) or the flooding limit may be thought
of as the flow condition at which the strong interaction between the two...
The pressure drop of convective boiling flow may be reduced by extracting vapor locally since the entire generated vapor does not have to travel through the entire channel length. In this study, the theoretical model was developed to simulate a convective boiling flow through a fractal-like branching microchannel network with...
This thesis addresses numerical simulation of flow maldistribution in microchannels. Microchannels are often associated with two phase-flows which can generate many problems such as plugging the channel or perturbing the flow. In this study we have used CFD and fully resolved technique to simulate what would happen in the case...
With the miniaturization of microelectronics and increase of processor speeds in the last few decades, thermal management is drastically affecting overall packaging and system capabilities. Due to the special needs introduced, research focusing on microscale cooling has increased. This study combines the positive characteristics of single- and two-phase flows in...
Metal oxide nanocrystals have attracted significant interests due to their unique chemical, physical, and electrical properties which depend on their size and structure. In this study, a continuous flow microreactor system was employed to synthesize metal oxide nanocrystals in aqueous solution. Assembly of nanocrystals is considered one of the most...
With continued development of the electronic industry, the demand for highly efficient heat removal solutions requires innovative cooling technologies. A computational fluid dynamic (CFD) study, including heat transfer, is performed for an axisymmetric, confined jet impingement experiencing boiling and coupled with vapor extraction. Boiling occurs at the target surface while...
The Oregon State University (OSU) Advanced Plant Experiment (APEX) is a one-fourth height, one-half time scale, reduced pressure integral systems test facility designed to model the long-term cooling capabilities of the emergency core cooling systems of the Westinghouse AP600. This study provides a brief description of the APEX test facility,...
A literature review of current phase separation publications was conducted. Data sets were collected and compiled into a Two-Phase Flow Separation Database. Examination of this database indicating a need for further investigation into the liquid entertainment phenomena for smaller hot-leg to branch diameters and intermittent flow regimes. A detailed analysis...
Advances in electronics fabrication, coupled with the demand for increased computing power, have driven the demand for innovative cooling solutions to dissipate waste heat generated by these devices. To meet future demands, research and development has focused on robust and stable two-phase heat transfer devices. A confined impinging jet is...
Two-phase flow in helical conduits is important in many industries where reaction between components, heat transfer, and mass transport are utilized as processes. The helical design is chosen for the effects of secondary flow patterns that reduce axial dispersion, increased heat transfer, and also their compact design. The first is...
The research presented in this thesis is a continuation of collaboration between Oregon State University and Auburn University studying the feasibility of passively pumping liquid during boiling in a preferential direction using meso-scaled asymmetric surface patterns. Such a passive phase-change mechanism has great potential for thermal management in spacecraft and...
In-situ vapor extraction is performed by applying a pressure differential across a hydrophobic porous membrane that forms a wall of the channel as a means of reducing the local quality of flow boiling within the channel. As the local quality is reduced, the heat transfer capability can be improve while...
Multi-phase flow in porous media includes many instances of subsurface flow. Three-phase flow in particular is important in situations of enhanced oil recovery, CO2 sequestration, and groundwater remediation. Many studies have been performed on how two fluid phases (oil/water or air/water) behave in porous media, but very few studies exist...
The ever increasing requirements for heat dissipation in various thermal management applications such as computer chip cooling and high power electronics have necessitated the need for novel thermal management techniques. Thermal management using heat sinks with microscale features is amongst the prominent techniques developed over the past two decades. In...
Recent advances in imaging technology and numerical modeling have greatly enhanced pore-scale investigations of multiphase flow and transport in porous media. It is now feasible to obtain high resolution 3-dimensional pore-scale data, and numerical methods such as the lattice-
Boltzmann (LB) technique have been developed specifically for simulating such phenomena....